A group of scientists at the University of Texas have developed a modified enzyme that can break down plastic in just a few days. It usually takes a long time for the plastic to completely degrade.
The the findings of the researchers were published last week in the scientific journal temper nature† The study used machine learning to create mutations in a fast-acting protein that can break down the building blocks of polyethylene terephthalate (PET). PET is a synthetic resin used in clothing fibers and plastics. According to the study, this substance is responsible for 12 percent of global waste.
The plastic has been broken down through a process called depolymerization. In this process, the catalyst separates the building blocks that make up PET into its original monomers, which are organic molecules. Those monomers can then be repolymerized to produce new plastics that can be incorporated into other products. What’s even more impressive about this process is that the enzymes can break down plastic within a week.
“We can break it down into its original monomers,” Hal Alper, professor of chemical engineering and author of the article, told VICE by phone. “That’s what the enzyme does. Once you have that original monomer, it’s like making new plastic from scratch, with the advantage that you don’t have to use extra oil.”
“This has advantages over traditional recycling,” Alper added. “If you melt the plastic and then reshape it, the plastic will lose its integrity with each new one. But if you are able to depolymerize and then chemically re-polymerize, you can make a new PET plastic each time.”
Their work complements the current series of studies on plastic-eating enzymes, which were first discovered in 2005. Since then, 19 more enzymes have been discovered, the article said. These enzymes come from naturally occurring bacteria found on plastic.
Many of these naturally occurring enzymes are composed of advanced proteins that function well in their own environment, but are limited by temperature and pH conditions. As a result, they simply cannot be used in any environment, such as in recycling centers, say the authors. In contrast, the enzyme discovered by Alper and his team is able to break down 51 types of PET over a range of temperatures and pH conditions.
The researchers called the enzyme FAST-PETase, short for Functional, Active, Stable, Tolerant PETase, and they worked out the exact structure using machine learning. An algorithm was fed 19,000 protein structures and learned to predict the positions of amino acids in the structure. They also used the formula to rearrange the amino acids of existing PETase species into new positions, and to identify improved groups of amino acids. The researchers came up with a structure that showed 2.4 times more activity than PETase at 40°C and 38 times more activity at 50°C.
Then it was tested at different temperatures and different pH levels, and it continued to perform well.
“What you see in nature is probably somewhat optimal, at least in the local environment around each of those amino acids,” Alper says. “We can start by looking at the protein we are interested in and then reviewing each of the amino acids. The microenvironment of those amino acids will tell what works and what doesn’t.”
Alper and his team hope that their enzyme is more scalable than most and that PETase can make a difference in tackling the global plastics crisis. FAST-PETase can handle a range of different conditions, but it must now be demonstrated that it can be “portable and affordable on a large industrial scale”.
First, says Alper, he and his team need to test FAST-PETase on the many different types of PET found in sewers. It should also be tested for waste that is usually found in plastic bottles or on top of plastic packaging during the recycling process. If researchers find an enzyme or group of enzymes powerful enough to be used in practice, they say it could help withbillions of tons“Treatment of waste in our environment.
